Abstract

We experimentally studied enhancement of the third-order
nonlinear optical phenomena, i.e., self-phase modulation due to optical Kerr
effect and two-photon absorption (TPA) in a small group-velocity (Vg) linedefect guided-mode of AlGaAs-based photonic-crystal slab waveguide. We found that the phase shift ∆φ or nominal Kerr constant n’2 and TPA coefficient β were strikingly enhanced due to small Vg as the band edge was approached, such that they were proportional to (Vg)-2; the nonlinear refractive index n2 is enhanced proportional to Vg-1. We also observed that owing to this enhancement as well as an extremely small cross-section area, the energy required for inducing π-phase shift was very small, being of an order of a few pJ for 5 ps optical pulse and for a 0.5-mm long sample. Based on those results, we discuss the possibility of developing ultra-fast and ultrasmall all-optical switches that operate due to cross-phase modulation.

Figures (9)

(a). The calculated W1 line-defect band (dotted curve) in Al0.26Ga0.74As photonic-crystal slab waveguide; the hatched area denotes the range in which the incident laser wavelength is varied. (b) The transmittance spectrum of a sample observed in a range including the guided modes (hatched area).

Variation of group refractive index ng=c /Vg with wavelength in a wavelength range near the band edge of the line-defect guided-mode in a PhC WG. The solid curve denotes the theoretical one; the dotted curve is the dispersion of Vg.

Required coupled power Pπ(n2) for yielding π phase shift as a function of wavelength. A theoretical one (solid curve) estimated on the basis of Eq. (4) is also presented for comparison. For detail, see the text.